Chemotactic cytokines (chemokines) are a class of potent inflammatory mediators that have the potential to attract specific subsets of leukocytes to sites of inflammation. Chemokines are typically low molecular mass (7–9 kD) proteins that can be divided into four subfamilies based on their primary amino acid structure. The CXC subfamily is characterized by the two conserved Cys (C) residues near the N-terminus, which are separated by an amino acid (X). Some of the CXC chemokines, such as IL-8 and growth related oncogene alpha (GRO-α), belong further to the ELR+ subfamily (Glu-Leu-Arg) and are important in the recruitment and activation of neutrophils.
The interaction of chemokines with specific cell populations is mediated by G-protein-coupled seven-transmembrane receptors (7TMR). Chemokine receptors can be classified into four groups (CR, CCR, CXCR, CX3CR) based upon their primary amino acid sequence. The CXCR1 receptor binds with high affinity to interleukin 8 (IL-8) and low affinity to NAP-2, ENA-78 (epithelial cell-derived neutrophil-activating factor), GRO-α, GRO-βand GRO-γ, whereas CXCR2 binds with high affinity to all of the afore-mentioned CXC chemokines. Both CXCR1 and CXCR2 receptors are found primarily on neutrophils and a subset of T-cells. See, e.g., Holmes, W., et al., Science (1991), Vol. 253, p. 1278; Murphy, P., et al., Science (1991), Vol. 253, p. 1280; Chuntharapai, A., et al., J. Immunol. (1994), Vol. 153, p. 5682; and Xu, L., et al., J. Leukocyte Biol. (1995), Vol. 57, p. 335. High levels of IL-8 and tissue neutrophil infiltration have been observed in the synovial tissues of rheumatoid arthritis patients (Endo, H., Lymphokine Cytokine Res.(1991), Vol. 10, p. 245). Evidence has been presented that GRO-αand IL-8 are important mediators involved in the recruitment of neutrophils in the early and late phase of lipopolysaccharide-induced (LPS) rabbit arthritis (Matsukawa, A, et al. Lab. Invest. (1991), Vol. 79, p. 591). The murine CXCR2 receptor has also shown to be necessary for neutrophilic inflammation in a mouse model of gouty synovitis (Terkeltaub, R., et al., Arthriti. Rheum. (1998), Vol. 41, p. 900. 41:900)
CXC chemokines have attracted attention as being important in the development of atherosclerosis (Terkeltaub, R., et al., Curr. Opin. Lipido.l(1998), Vol. 9, p. 937). The role of CXCR1 and CXCR2 ligands on monocyte function in atherosclerosis in rabbits was published by Schwartz, D., et al., J. Clin. Invest. (1994), Vol. 94, p. 1968. Knockout mice that lacked CXCR2 expression had diminished lesion size (Boisvert, W., et al., J. Clin. Invest. (1998), Vol. 101, p. 353). The involvement of the CXCR2 receptor in the pathological inflammatory response elicited by central nervous system (CNS) cells as related to Alzheimer's disease is also gaining significant attention (Xia, M., et al., J. Neurovirol. (1999), Vol. 5, p. 32). Reports have focused on the upregulation of CXCR2 expression on dystrophic neurites of senile plaques. See, e.g., Xia, M., et al., Am. J. Pathol. (1997), Vol. 150, p. 1267, and Horuk, R., et al., J. Immunol. (1997), Vol. 158, p. 2882.
High levels of IL-8 and neutrophil infiltration have been observed in the pathogenesis of a number of other disease indications. This includes ulcerative colitis (Mahida, Y., et al., Clin. Sci. (1992), Vol. 82, p. 273, and Izzo, R., Am. J. Gastroenterol. (1992), Vol. 87, p. 1447) and psoriasis (Gillitzer, R., et al., J. Invest. Dermatol. (1996), Vol. 107, p. 778 and Kojima, T., J. Invest. Dermatol. (1993), Vol. 101, p. 767). CXCR1 and CXCR2 chemokines and their roles in tumor growth and metastasis have been reviewed. See, e.g., Wang, J., J. Immunol. Meth. (1998), Vol. 220, p. 1.
To date, a limited number of CXCR1 and CXCR2 receptor antagonists have been reported. It was reported that a bis-aryl urea was able to selectively inhibit CXCR2 receptor and prevent neutrophil margination and chemotaxis in a rabbit model. See, e.g., White, J., J. Biol. Chem. (1998), Vol. 273, p. 10095. Other CXCR1 and CXCR2 receptor antagonists have focused on NH2-terminal truncations and modifications of IL-8, GRO-α, and ELR motif (Jones, S., et al., J. Biol. Chem., Vol. 272, p. 16166). Murine neutrophil recruitment in vivo could also be inhibited via CXCR2 receptor blocking using a truncated human GRO-αanalog. There are currently no CXCR1 or CXCR2 receptor antagonist based therapies widely available.
There is a continued need for the treatment of diseases mediated by the CXCR2 receptor. Small molecule antagonists of the CXCR2 receptor and their ligands, such as GRO-αand IL-8, would be useful in the control of harmful inflammatory processes as well as important tools for the investigation of receptor-ligand interactions.